GM wanted Rivian all to itself, but the electric vehicle startup wanted to play the field.

Now, hopes for a May-September marriage between the two automotive companies appear to have faded away.

Rivian, the darling of last year's Los Angeles Auto Show based in Detroit's backyard, still has the backing of package delivery behemoth Amazon, but Bloomberg is reporting that talks with GM have broken down, apparently over a desire for monogamy.

"... Rivian is rebuffing a deal that may have required a level of exclusivity that would have kept it from building vehicles for others," according to the news service.

Rivian Lead Design Sculptor Andrew Frierott works on design development for an R1T electric vehicle at the startup in Plymouth on Thursday, February 21, 2019.(Photo: Ryan Garza, Detroit Free Press)

Sadly, monogamy only works if both sides truly want it.

A spokesman for Rivian, which is based in Plymouth Township, declined to comment on the issue.

But Rivian founder and CEO RJ Scaringe, in his interview with Bloomberg at the New York Auto Show, might have hinted at why things fell apart.

“In general, my reason for starting Rivian was to do big things without anything preventing us from doing that," he told the news service.

GM spokesman Pat Morrissey provided a company statement "on reports that the rumored talks between GM and Rivian have broken off," which was neither a confirmation nor a denial.

"As we have stated, we admire Rivian's contribution to a future of zero emissions and an all-electric future. Talks occur on a regular basis in the auto industry between a variety of partners, but as a matter of policy we don’t discuss who, where or when those discussions might occur."

Bloomberg noted that had the companies reached a deal, GM could have provided its engineering and manufacturing expertise, and Rivian could have helped GM "get an electric pickup to market quicker."

Rivian, which moved from Florida's Space Coast to metro Detroit in 2013, unveiled an electric pickup and SUV at the LA Auto Show. The company, which had about 750 employees at its various locations in February, has touted a possible 400-mile-per-charge battery range and been dubbed a "Tesla killer" by some industry watchers. Its focus, however, is on building vehicles for the active lifestyle set; it expects to deliver its vehicles to customers starting late next year.

Despite the apparent end of talks with Rivian, GM has its own electric vehicle plans. Last month, the Free Press reported that the company would spend $300 million to build a new electric car at its Orion Assembly Plant.